1. Field of the Invention
This invention relates to systems for providing electronic documents, and more particularly to document delivery systems wherein servers transcode documents delivered to client machines.
2. Description of Related Art
The World Wide Web, known simply as the “Web”, is a network of Internet servers that provide specially formatted electronic documents to various “client” machines. Web servers currently support documents formatted in a text-based markup language called hypertext markup language (HTML).
In order to provide Web access to client machines with limited capabilities (e.g., palmtop or handheld computers), a “transcoder proxy” is typically positioned between the client machine and an Internet server. The transcoder proxy may, for example, provide selected portions of a requested Web document to the client machine based upon the capabilities of the client machine. In doing so, the transcoder proxy may translate one or more selected portions of the Web document from one digital format to another.
FIG. 1 is a block diagram of a representative system 10 currently used to provide an electronic document 12 (e.g., a Web page) to a client machine 14 with limited capabilities. Client machine 14 may be, for example, a palmtop or handheld computer with limited memory, processing capability, and/or display capability. System 10 includes an internet server 16, and a transcoder proxy 18 interposed between client machine 14 and internet server 16. Transcoder proxy 18 forwards a request for document 12 from client machine 14 to internet server 16. Such a request typically includes a uniform resource locator (URL) of document 12 specifying the internet protocol (IP) address of document 12 and the name of the file containing document 12.
Internet server 16 fetches document 12 and provides document 12 to transcoder proxy 18. Based upon the capabilities of client machine 14, transcoder proxy 18 may translate or “transcode” one or more selected portions of document 12 from one digital format to another. For example, transcoder proxy 18 may transcode a portion of document 12 from HTML to a script written in a scripting language understood by a Web browser application program running within client machine 14. The Web browser program may use information conveyed by the script to present the one or more selected portions of document 12 upon a display device of client machine 14.
Alternately, client machine 14 may include a text-to-speech converter, and the information conveyed by the script may be used to output the one or more selected portions of document 12 as speech through a speaker of client machine 14. The term “assistive technology” is used herein to describe technology that helps physically challenged individuals access to a computer system (e.g., client machine 14). Well known types of assistive technologies include “screen readers” which convert display information to speech, “screen magnifiers” which enlarge features of portions of display screen contents, and voice recognition software which converts speech to a digital representation of text or commands.
Computer language code or “script” which modifies visual presentations of electronic documents in response to user input is increasingly being included within electronic documents. Such interactive aspects of electronic documents are used to provide, for example, Web site navigation information in response to user input. JAVASCRIPT (™ Netscape Comm. Corp., Mountain View, Calif.) is a well known cross-platform, object-based scripting language for client and server applications. JAVASCRIPT is commonly used to add interactive aspects to electronic documents such as Web pages.
The Document Object Model (DOM) is an application programming interface (API) for “documents”. The World Wide Web Consortium (W3C) has authored a DOM specification available on the Web at URL http://www.w3.org/. The DOM defines the logical structure of documents and the way a document is accessed and manipulated. In the DOM specification, the term “document” is used in the broad sense. Increasingly, XML is being used as a way of representing many different kinds of information that may be stored in diverse systems. Much of this information would traditionally be seen as data rather than as documents.
In the DOM, documents have a logical structure which is very much like a tree. To be more precise, the logical structure is like a “forest” or “grove”, which can contain more than one tree. However, the DOM specification does not require that documents be implemented as a tree or a grove, nor does it specify how the relationships among objects be implemented. The DOM is a logical model that may be implemented in any convenient manner. In the DOM specification, the term “structure model” is used to describe the tree-like representation of a document. Terms like “tree” or “grove” are not used to avoid implying a particular implementation. One important property of DOM structure models is structural isomorphism. If any two DOM implementations are used to create a representation of the same document, they will create the same structure model, with precisely the same objects and relationships.
In current document delivery systems, a problem arises in that many client machines do not support interactive aspects of electronic documents such as Web pages due to resource limitations. As a result, transcoding proxy 18 may be configured to remove any computer language code or script within the one or more selected portions of an electronic document provided to client machine 14. Web site navigation capability may be lost, and with it the ability to access Web site information. Additionally, a client machine may not have sufficient resources to provide an assistive technology solution for a physically challenged user.
It would thus be desirable to have an electronic document delivery system which allows a client machine with limited resources to provide interactive aspects of electronic documents such as Web pages and/or an assistive technology solution for a physically challenged user. The desired document delivery system may use the document object model (DOM) to define a logical structure of an electronic document, and to access and manipulate the electronic document.